1. Field of the Invention
The invention relates to an image data processing, and more particularly, to an image scaling processing.
2. Description of the Prior Art
Display apparatus such as TVs, LCD monitors, plasma monitors, and projectors, etc. can be used for displaying static images or dynamic videos. Different video formats usually have different resolutions. For example, the resolution of Video Graphics Array (VGA) is 640*480. The resolution of a Super Extended Graphics Array (SXGA) is 1280*1024. Under the condition that the resolution of the display apparatus is different from the resolution of the received video signals, the received input video images must first be scaled in order to display the correct video images.
The conventional scaling method can use a frame buffer or a line buffer to store the received frame and scales (ex: perform an interpolation operation) a plurality of pixels of the received frame from the frame buffer or the line buffer.
In the above-mentioned conventional method, an interpolator which includes a scaling filter having a fixed number of filter taps is used to perform the interpolation operation. Take the filter having 5 fixed taps as an example. Every time generation of an output horizontal line is required, the 5 taps of the scaling filter are used to respectively receive 5 input horizontal lines in the input video (ex: 4 of the input horizontal lines are already received and stored in the four line buffers, and another horizontal line is the input scan line currently being received). In order to complete the above-mentioned interpolation operation, the conventional scaling apparatus must have at least 4 horizontal line buffers, wherein each of the scan line buffers has a storage space for storing an input horizontal line. However, since the input video may have various different format (resolutions) and the image scaling apparatus need to be able to process the input videos with said various different resolutions, the strictest condition (i.e. the condition where the input video has the largest resolution) has to be considered when designing the image scaling apparatus. For example, if the input maximum resolution that the conventional scaling apparatus can process is 1920*1080, and the amount of the tap of the scaling filter of the conventional scaling apparatus is fixed to be 5, then the conventional apparatus must have at least 4 line buffers where each line buffer can store 1920 pixel data. In other words, a storage space of the conventional apparatus that can store 7680 pixel data in total is required, and this is a large hardware cost. In this example, when the conventional scaling apparatus receives an input image which has 640*480 resolution, the storage space of the conventional apparatus that can store 7680 pixel data only store 2560 (640×4) pixel data because the tap of the scaling filter of the conventional apparatus is fixed to be 5. Furthermore, the quality of the scaled image is better when the number of filter taps of the scaling filter is larger.